This evaluation ignores the consequentialist result of holding "entering into a war is never justified" as a major worldview/national policy. If you view wars of retaliation as a necessary expense to maintain a credible threat of retaliation, it changes the equation completely. That is, failing to retaliate would send the message, "You can always get away with attacking us," the cost of which, over time, would probably significantly outweigh the cost of any specific war of retaliation.